1. Field of the Invention
The present invention relates to a drive connection mechanism to connect a drive unit and a driven unit. In particular, the present invention relates to a drive connection mechanism to connect a photoconductive drum of a copier or printer and its drive shaft, and an image forming apparatus having the drive connection mechanism.
2. Description of the Related Art
In a known drive connection mechanism to connect a photoconductive drum of a copier to a drive shaft provided in a main body of a copier, a coupling gear is provided rotatably together with a drive shaft and slidably along the axial direction of the drive shaft. In the periphery of the coupling gear, outer bevel gear is formed coaxially with the drive shaft. The coupling gear is energized toward the distal end of the drive shaft by a compression spring fit to the drive shaft. At the corresponding end of the photoconductive drum, internal gears like a bevel gear are formed to engage with the external gears of the coupling gear.
Therefore, when connecting the drive shaft to the photoconductive drum, fit and push the coupling gear of the drive shaft in the internal gears of the photoconductive drum, and press the external gears of the coupling gear to the internal gears of the photoconductive drum by the restoring force of the compression spring. The external gears of the coupling gear are securely engaged with the internal gears of the photoconductive drum, the driving force of the drive shaft is transmitted to the photoconductive drum, and the photoconductive drum is driven by the drive shaft.
However, in the above-mentioned drive connection mechanism, as the coupling gear is provided slidably along the drive shaft, the coupling gear can be securely engaged with the internal gears of the photoconductive drum, but a clearance exists between the coupling gear and causes a backlash. Namely, the clearance causes a backlash when the driving force is transmitted from the drive shaft to the photoconductive drum.
To eliminate a backlash of the coupling gear to the drive shaft, the inventor of this application proposes a drive connection mechanism which divides the coupling gear having the above described form into three parts in the circumferential direction (Jpn. Pat. Appln. KOKAI Publication No. 8-87225).
The drive connection mechanism has an involute spline extending in the axial direction on the periphery of a drive shaft, and has grooves to engage with the involute spline inside each coupling gear divided into three. When three coupling gears are energized in the axial direction and pressed to the internal gears of the photoconductive drum by a compression spring, each coupling gear receives repulsion toward the drive shaft from the internal gears like a bevel gear of the photoconductive drum, and each coupling gear is pressed to the drive shaft by this repulsion. Therefore, each coupling gear is securely engages with the drive shaft, and the above-mentioned backlash can be decreased.
By using the above conventional drive connection mechanism, a backlash can be decreased and a driving force can be transmitted from the drive shaft to a photoconductive drum, but the centering of the photoconductive drum and drive shaft is insufficient, the photoconductive drum swings a little during rotation, and a satisfactory image is not formed.